1. Field of the Invention
This invention relates to four-way directional control air valves of the type used in the control of the flow of pressurized air to and from various apparatuses, such as an air cylinder, and similar devices.
2. Description of the Prior Art
It is known in the prior art to provide four-way differential air control valves which have a valve spool that is moved in one direction by pilot air, and in the other direction by a return spring, or movable in two opposite directions by pilot air. A disadvantage of the prior art four-way valves is that they include two exhaust chambers in the valve spool bore which involve complicated flow paths through the valve body for combining the two exhaust chambers and connecting them to an exhaust outlet port. The prior art requirement of two exhaust chambers in the valve spool bore of the valve results in many restrictions in the exhaust flow path which detracts from the operating efficiency of an air valve. A further disadvantage of said prior art air valves is that the air supply chamber in the valve spool is normally positioned in the center of the valve spool bore, and such a position is a disadvantage where the valve main air supply must also be conducted internally to the ends of the valve body for conduction to one or more pilot air valves for operating the main valve spool in the spoolvalve.